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Transcript of WiMAX Class
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TELCORDIA TECHNOLOGIES, INC. PROPRIETARY - INTERNAL USE ONLY
This document contains proprietary information that shall be distributed, routed or made available only within Telcordia, except with written permission of Telcordia.
WiMAX OverviewContact:
Andrew Burnette
Principal Analyst
Phone Number
908.565.3740
October 8, 2009
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References IEEE 802.16-2004 (802.16REVd)
IEEE 802.16-2005 (802.16e)
Intel‟s Whitepapers, 2004(http://www.intel.com/technology/itj/2004/volume08issue03/)
“IEEE Standard 802.16: A Technical Overview of the WirelessMAN Air Interface for Broadband Wireless Access,” C. Eklund et al., IEEECommunication Magazine, June 2002
“Broadband Wireless Access with 802.16/WiMax: CurrentPerformance Benchmarks and Future Potential,” A. Ghosh et al.,IEEE Communication Magazine, Feb 2005
“Wireless Communication Standards: A Study of IEEE 802.11,
802.15, and 802.16,” T. Cooklev, 2004
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4G Wireless – WiMAX
WiMAX-- Worldwide Interoperability for Microwave Access
Multiple Input and Multiple Output (MIMO)MIMO channel capacity is given by
C = B log2 det(I + SNR.HH*T/N)
where H is MxN channel matrix with M and N are receiveand transmit antennas, resp.
Hybrid-ARQFor faster ARQ, combines error correction and detection andmakes use of previously received versions of a frame
Adaptive Antenna System (AAS)Enables directed beams between BS and SSs
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Physical layer
Implement Orthogonal Frequency Division Multiplexing
Configurable parameters are:
Transmission power
Cyclic Prefix
Frequency
Frequency bandwidth
Modulation (BPSK, QPSK, 16QAM, and 64QAM)
Computed values:
Sampling frequency
OFDM symbol time duration Transmission time for a packet according to its size and the modulation
used
Maximum packet size for a given modulation and number of availableOFDM symbols
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MAC layer
Time Division Duplexing (TDD)
Management messages for network entry:
DCD/UCD, DL_MAP/UL_MAP
Ranging request/response
Registration request/response
Flow management: currently add one downlink and one uplink dataconnection per SS.
Extensible scheduler (currently Best Effort+Round Robin)
Fragmentation/Reassembly of packets
Mobility Extension (802.16e): Neighbor advertisements
Scanning and handover
IEEE 802.21 ready (trigger configuration and generation)
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MAC layer configuration
Frame duration
DCD/UCD interval
Burst modulation
Channel
Contention size
Scanning attributes (number of iterations, duration)
Frequency of neighbor advertisements
Statistics (used for trigger generation)
Loss
Delay Jitter
throughput
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Advantages in Multipath
OFDMA carries advantages in “Multipath” CDMA uses the whole spectrum, wasting system resource to combat frequency
selective fading.
CDMA also creates worse interference problem
OFDMA only select subcarriers with less channel degradation, prevent wasting
system resource (power or throughput ) => achieving higher system capacity.
Signal Sent
Signal Received
Multipath
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Spectral Efficiency Wins
2.5G TDMA: Very limiteddata rate and low spectralefficiency (1.0-1.5 bps/Hz)
500kHz 5MHz
3G WCDMA: Reasonabledata rate, range, andmobility, improved spectralefficiency (1.5-2.5 bps/Hz)
WiFi: OFDM 64FFT,Reasonable data rate,limited range and mobility,improved spectralefficiency (2-3 bps/Hz)
WiMAX:OFDMA, Up to2048FFT much improvedrange and mobility,potential for bestspectral efficiency (3-4bps/Hz)
15 MHz20 MHz
Spectrum efficiency is an important factor for data service The scarce of available (or useful) spectrum makes efficiency a key factor to approve
spectrum and the success of business model.
Regulatory bodies shall recycle spectrum for existing systems with low spectral
efficiency.
Future systems with high spectrum re-use advantages or higher spectral efficiency
shall have favored allocation during application.
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OFDMA principle
OFDM modulation can be realized with efficient Inverse Fast
Fourier Transform (IFFT), which enables a large number of
sub-carriers (up to 2048) with low complexity. The opposite
function is carried out by FFT at receive end.
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OFDMA Symbol StructureThe OFDMA symbol structure consists of three types of sub-carriers as
shown in Figure.
Data sub-carriers for data transmission
Pilot sub-carriers for estimation and synchronization purposes
Null sub-carriers for no transmission: DC carriers
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Example with 1024 Sub-Carriers
1024 samples in 91.4 uS
(only 720+120 in use for data + Pilot)
11.4 uS
102.9 uS
1024 sub-carriers with spacing of
1/91.4 uS = 10.94 KHzGuard Band
Sampling frequency = 10.94 KHz x 1024 = 11.2 MHz
Bandwidth used: 10.94 x (720 +120) = 9.18 MHz
Data rate = (1024 x 2) / 102.9 uS = 14 Mbps(based on 16 QAM and ½ coding)
OFDM Symbol frequency = 1 / 102.9 uS = 9.72 KHz
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WiMAX : Special Advantages
All systems support HARQ, Scheduling and Virtual Soft
Hand off. WiMAX however supports:
Tolerance to Multipath and Self-Interference
Scalable Channel Bandwidth
Orthogonal Uplink Multiple Access
Support for Spectrally-Efficient TDD
Frequency-Selective Scheduling
Fractional Frequency Reuse
Improved AMC and Error Correction Techniques Fine Quality of Service (QoS)
Advanced Antenna Technology
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OFDMA Scalability
OFDMA Scalability is obtained by adjusting FFT size depending on available
spectrum
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Uplink Orthogonality
OFDMA allows allocation of different portions of the channelso that there is no (or little) multiple access interference (MAI)between multiple users. OFDMA therefore, can support higher order uplink modulations and achieve higher uplink spectralefficiency. With CDMA, on the other hand, each user transmits
over the entire channel. Even though it is possible to constructorthogonal spreading codes, this is rarely done due to the uplinksynchronization issues.
Orthogonal uplink sub-channels also enables the uplinkscheduler to provide better control of the uplink quality and uplinkresource allocation. Therefore the uplink performance is morepredictable and QoS is better enforced.
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Support for TDD
In spite of need for system-wide frame synchronization, TDDoffers following advantages.
TDD enables adjustment of the downlink/uplink ratio on a per cluster basis to efficiently support asymmetric downlink/uplinktraffic – as required for all data applications.
TDD assures channel reciprocity for better support of linkadaptation, MIMO and other closed loop advanced antennatechnologies.
Unlike FDD, which requires a pair of channels, TDD only requiresa single channel for both downlink and uplink providing greater flexibility for adaptation to varied global spectrum allocations.
– Transceiver design for TDD implementations is less complex andtherefore less expensive.
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WiMAX TDD Structure
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802.16-e Frame
Unit allocation is large with smaller segment of
sub-carriers allocated to a user – improves
efficiency21
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Frequency Selective Scheduling
Both 1xEVDO and HSPA signals occupy entire bandwidth.Mobile WiMAX signals on the other hand only occupy a portionof the bandwidth. In broadband wireless channels, propagationconditions can vary over different portions of the spectrum indifferent ways for different users. Mobile WiMAX supports
frequency selective scheduling to take full advantage of multi-user frequency diversity and improve QoS. WiMAX makes itpossible to allocate a subset of sub-carriers to mobile usersbased on relative signal strength. By allocating a subset of sub-carriers to each MS for which the MS enjoys the strongest path
gains, this multi-user diversity technique can achieve significantcapacity gains over TDMA/CDMA.
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Frequency Reuse
Mobile WiMAX, 1xEVDO and HSPA all support frequency reuse
one, i.e. all cells/sectors operate on one frequency channel tomaximize spectrum utilization. However, due to heavy interferencein (common frequency) reuse „1‟ deployment, users at the cell edgemay suffer low connection quality.
1xEVDO and HSPA address the interference issue by adjustingthe loading of the network. However, the same loading factor is
applied to all users within the coverage area, leading to capacityloss by “over -protecting” users that are closer to the base station.
In WiMAX the sub-channel reuse pattern can be configured sothat users close to the base station operate on the zone with allsub-channels available. While for the edge users, each cell/sector operates on the zone with a fraction of all sub-channels available.23
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Fractional Frequency Reuse with WiMAX
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QoS Control
WiMAX QoS is specified for each service flow –up and down.The service flow parameters can bedynamically managed through MAC messages toaccommodate the dynamic service demand.Furthermore, since the sub-channels are
orthogonal, there is no intra-cell interference ineither DL or UL. Therefore, the DL and UL linkquality and QoS can be easily controlled by thebase station scheduler.
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QoS Control
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Applications with Different QoS
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Smart Antenna
In CDMA-based systems, the signals occupy the entirebandwidth. Since the processing complexity for smartantenna technologies scales with the channel bandwidth,supporting advanced antenna technologies in broadband
wireless channels poses a more significant challenge thanit does with Mobile WiMAX. Both 1xEVDO and HSPAsupport simple transmit diversity and the HSPA standardhas an option to support Beam-forming. In general
however, the use of advanced antenna technologies incurrent 1xEVDO and HSPA solutions has been limited.
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Continued -
Since OFDM/OFDMA converts a frequency selectivewideband channel into multiple flat narrow band sub-carriers itis far easier to support smart antenna technologies. MobileWiMAX supports a full range of smart antenna technologies toenhance performance including Beam-forming, STC (Space
Time Coding) and SM (Spatial Multiplexing). Thesetechnologies can improve both system coverage andcapacity.
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Continued -
WiMAX also supports dynamic switching between the smartantenna technologies to maximize the benefit based onchannel conditions. Spatial Multiplexing (SM) for example,improves peak throughput but, when channel conditions arepoor, the Packet Error Rate (PER) can be high and thus thecoverage area where target PER is met may be limited. SpaceTime Coding (STC) on the other hand provides large coverageregardless of the channel condition but does not improve thepeak throughput. Mobile WiMAX supports Adaptive MIMOSwitching (AMS) is used between multiple MIMO modes to
maximize spectral efficiency with no reduction in coveragearea
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MBS: Managed Bandwidth service,
CQICH: Channel Qual ity Indicator ChannelPKMv2: Private Key Management v2, EAP: Extensible Authentication Protocol
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EVDO, HSPA and WiMAX Parameters
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Mobile WiMAX OFDMA Parameters
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Thank you
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Comparison of WiMAX Rel-
d and Rel-e Fixed WiMAX: 802.16 – 2004 (802.16d)
150 fixed trials on 3.5 GHZ TDD and FDD
Universal WiMAX: 802.16 – 2005 (802.16e) Limited trials AT&T, CTC Telecom Wisconsin
and plans in middle East, Africa, Sri Lanka etc.
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WiMAX-d and WiMAX-e Profile
Comparision
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WiMAX-d Frame
Small unit allocation with full OFDM
symbol (all sub-carriers) allocated to a
user at a time53
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802.16-e Frame
Unit allocation is large with smaller segment of
sub-carriers allocated to a user – improves
efficiency54
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VoIP Improvements with 802.16-e
• Small Overhead with Header compression (Rel-d Overhead ~ 4 x payload)•Silence suppression with ertPS (Enhanced Real Tme Packet service)
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Advanced Antenna Technologies
Rel-d specifies advanced antenna
mechanism but not selected in profiles.
Similarly MIMO is limited to simple diversity
coding techniques (e.g. 2x1 Alamounti
scheme with 1 3 dB gain)
Rel-e profile supports multiple antenna
solutions starting with beam formingsolutions for cell range, interference and
capacity increase.56
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Interference Mitigation with Beam
Forming
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Li k B d t C i
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Link Budget Comparison(Rel-d / Rel-d+ and Rel-e)
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CDF vs SINR with and without Beam Forming
Rel-e provides more spectral efficiency and higher coverage59
Scheduling Services Usage and
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Scheduling Services, Usage and
QoS parameters
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WiMAX N t k R f M d l
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WiMAX Network Reference Model
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WiMAX N t k IP b d
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WiMAX Network - IP based
Architecture
COTS: Commercial Off The Shelf 62
WiMAX Downlink Budget
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g
PUSC: Partially Used Sub Carrier
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WiMAX Uplink Margin
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p g
PUSC: Partially Used Sub Carrier
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Mobile WiMAX Physical Data Rates
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WiMAX d and WiMAX e Profile
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WiMAX-d and WiMAX-e Profile
Comparision
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WiMAX-d Frame
Small unit allocation with full OFDM
symbol (all sub-carriers) allocated to a
user at a time
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802.16-e Frame
Unit allocation is large with smaller segment of
sub-carriers allocated to a user – improves
efficiency
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VoIP Improvements with 802.16-e
• Small Overhead with Header compression (Rel-d Overhead ~ 4 x payload)
•Silence suppression with ertPS (Enhanced Real Tme Packet service)
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Advanced Antenna Technologies
Rel-d specifies advanced antenna
mechanism but not selected in profiles.
Similarly MIMO is limited to simple diversity
coding techniques (e.g. 2x1 Alamounti
scheme with 1 3 dB gain)
Rel-e profile supports multiple antenna
solutions starting with beam formingsolutions for cell range, interference and
capacity increase.70
Interference Mitigation with Beam
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Interference Mitigation with Beam
Forming
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Link Budget Comparison
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Link Budget Comparison(Rel-d / Rel-d+ and Rel-e)
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CDF vs SINR with and without Beam Forming
Rel-e provides more spectral efficiency and higher coverage73
Scheduling Services, Usage and
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QoS parameters
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WiMAX Network Reference Model
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WiMAX Network Reference Model
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WiMAX Network - IP based
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WiMAX Network IP based
Architecture
COTS: Commercial Off The Shelf 76
WiMAX Downlink Budget
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PUSC: Partially Used Sub Carrier
77
WiMAX Uplink Margin
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PUSC: Partially Used Sub Carrier 78
M bil WiMAX Ph i l D t R t
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Mobile WiMAX Physical Data Rates
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